Abstract
Crystal (Cry) proteins made by the bacterium Bacillus thuringiensis are pore-forming toxins that specifically target insects and nematodes and are used around the world to kill insect pests. To better understand how pore-forming toxins interact with their host, we have screened for Caenorhabditis elegans mutants that resist Cry protein intoxication. We find that Cry toxin resistance involves the loss of two glycosyltransferase genes, bre-2 and bre-4. These glycosyltransferases function in the intestine to confer susceptibility to toxin. Furthermore, they are required for the interaction of active toxin with intestinal cells, suggesting they make an oligosaccharide receptor for toxin. Similarly, the bre-3 resistance gene is also required for toxin interaction with intestinal cells. Cloning of the bre-3 gene indicates it is the C. elegans homologue of the Drosophila egghead (egh) gene. This identification is striking given that the previously identified bre-5 has homology to Drosophila brainiac (brn) and that egh-brn likely function as consecutive glycosyltransferases in Drosophila epithelial cells. We find that, like in Drosophila, bre-3 and bre-5 act in a single pathway in C. elegans. bre-2 and bre-4 are also part of this pathway, thereby extending it. Consistent with its homology to brn, we demonstrate that C. elegans bre-5 rescues the Drosophila brn mutant and that BRE-5 encodes the dominant UDP-GlcNAc:Man GlcNAc transferase activity in C. elegans. Resistance to Cry toxins has uncovered a four component glycosylation pathway that is functionally conserved between nematodes and insects and that provides the basis of the dominant mechanism of resistance in C. elegans.
Highlights
Bacterial pore-forming toxins that damage membranes are important virulence factors associated with pathogenic bacteria [1, 2]
We find that Cry toxin resistance involves the loss of two glycosyltransferase genes, bre-2 and bre-4
Like in Drosophila, bre-3 and bre-5 act in a single pathway in C. elegans. bre-2 and bre-4 are part of this pathway, thereby extending it
Summary
Crystal; ORF, open reading frame; HA, hemagglutinin. 2 L. We find that bre-2 and bre-4 function in the intestine to confer susceptibility to Cry5B and are required for the interaction of toxin with intestinal cells in vivo. We identify the bre-3 resistance gene as sharing significant homology to Drosophila egghead (egh). Because bre-5 shares sequence similarity to the Drosophila brainiac (brn) gene and since egh and brn function in a single pathway in Drosophila, we hypothesized that the Cry protein intoxication pathway in C. elegans is equivalent to the Drosophila pathway. We show that bre-3 and bre-5 function in a common pathway in C. elegans, that bre-2 and bre-4 are part of this pathway, and that the C. elegans bre-5 gene has the same in vivo and in vitro activities as Drosophila brn
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